Pharmaceutical formulation comprising melatonin

ABSTRACT

Short-term potentiation of non-barbiturate and non-benzodiazepine hypnotics is effected by use of melatonin.

FIELD OF THE INVENTION

The present invention relates to use of melatonin in the manufacture ofmedicaments for short-term potentiation of certain hypnotics, and topharmaceutical formulations comprising melatonin and such hypnotics.

BACKGROUND OF THE INVENTION

Gamma-aminobutyric acid (GABA) acting via GABA-A receptors is thebrain's major inhibitory neurotransmitter system and exerts a crucialrole in regulating brain excitability. GABA-A receptors comprise fivesubunits. The different protein subunits that make up the receptor forthe inhibitory neurotransmitter gamma-aminobutyric acid (GABA) have beenidentified, and make up the alpha, beta, gamma and delta families, foreach of which exist several subtypes. The subunit make-up of a receptor,particularly its alpha-subunit content, determines its pharmacologicalcharacteristics. A number of drugs interact with binding sites ondifferent subunits of the GABA-A receptors, and these include modemhypnotic drugs (i.e. benzodiazepines, and the newer non-barbiturate andnon-benzodiazepine agents, e.g. imidazopyridines and cyclopyrrolones),as well as anticonvulsants, anaesthetics and neurosteroids (e.g. theprogesterone metabolite pregnalone).

Receptor subtype specificity of hypnotics has been explained in terms ofdifferential affinity for receptors containing different alpha subunits,which are expressed in different brain regions. Thus, receptors thatinclude an alpha1 subunit have a type (I) pharmacology and bind thenon-barbiturate and non-benzodiazepine agents zolpidem and zaleplon withhigh affinity, whilst receptors with alpha2, alpha3 or alpha5 subunitshave a type (II) pharmacology and bind these drugs with low affinity.Both type (I) and (II) bind diazepam and other benzodiazepines. Incontrast, receptors that contain alpha4 and alpha6 subunits, arediazepam-insensitive. The ligand selectivity of receptor subunitsassists in their characterization. Site-directed mutagenesis hasindicated that benzodiazepines bind to a cleft on the GABA-A receptorsurface at the interface between the alpha and gamma subunits. Otherdrugs (flumazenil, zopiclone, zolpidem) also bind to the alpha subunit,but interact with amino acids in different binding domains to thebenzodiazepines.

Using immunochemical and ligand-binding techniques, the subunitcomposition of GABA-A receptors has been shown to exhibit a degree ofbrain regional specificity. The predominant GABA-A receptor compositionfound in the brain is alphalbeta2gamma2, which are all encoded on humanchromosome 5. Targeted gene disruption has provided clues to thephysiological functions served by GABA-A receptors containing differentsubunits. Receptors containing gamma2 appear to have a vital role inmaintaining appropriate central inhibition, beta3-containing receptorsmay also be important determinants of excitability in, certain brainregions, whereas a clear role for alpha5-, alpha6- and gamma3-containingreceptors has not yet been established by these techniques.

GABA-A receptors are of great clinical significance in severaldisorders, including insomnia, epilepsy, anxiety and alcoholism;benzodiazepines are used commonly to treat anxiety, and studies suggestthat benzodiazepine antagonists and inverse agonists (which induce theopposite effect to agonists at receptors) may be useful in alcoholrehabilitation.

Among the most prominent uses of GABA-A receptor modulators(benzodiazepines and non-benzodiazepine hypnotics) is the treatment ofinsomnia, defined as problems initiating and/or maintaining sleep, atleast three nights/week accompanied by daytime distress or impairment.Persistent insomnia is associated with an array of individual andsocietal consequences, including greater medical and psychiatricmorbidity, life-threatening accidents, reduced quality of life, impairedjob performance, and absenteeism. Insomnia is associated with negativeconsequences for health-related quality of life, daytime well-being, andalso has economic implications. The cost of insomnia in terms of lostproductivity and accidents has been estimated at $77-$92 billionannually.

Benzodiazepines are very potent in sleep induction (shortening sleeplatency) and maintenance (increasing total sleep time). These drugs havehowever detrimental effects on awakening from sleep (hangover effects)and daytime vigilance (psychomotor functioning), the next morning. Thenewer non-barbiturate and non-benzodiazepine hypnotic agents (e.g.imidazopyridines and cyclopyrrolones) have been available since the late1980's and have been proposed as an alternative strategy. These shortensleep latency and do not produce major “hangover” effects the nextmorning. The possible adverse effects of these sleep aids includeresidual sedation and psychomotor impairment, daytime anxiety,anterograde amnesia and cognitive impairment, rebound insomnia, and drugtolerance and dependence. Because patients may experience daytimesleepiness there is a potential for impaired performance and anincreased risk of accidents, particularly of traffic accidents. Allbenzodiazepines adversely affect cognition by disrupting both short andlong term memory. Episodic, semantic and iconic memory are impaired.Former use of benzodiazepines is associated with a significantlyincreased risk of dementia in elderly persons (65 years of age andolder). The degree of memory loss is a function of the specific agentand dose. Therefore, lowering the dose of these agents, whilemaintaining their hypnotic effects, may be beneficial to circumventthese impairments.

The development of dependence on these drugs is also a matter ofconcern. The molecular mechanism of hypnotic dependence has beenexplored, and seems to involve down-regulation of transcription of thenormally prevalent alpha1, beta2 and gamma2 subunits, and the reciprocalup-regulation of the expression of rarer subunits. Zolpidem is animidazopyridine agent that is indicated for the short term (up to 4weeks) treatment of insomnia, at a recommended dosage of 10 mg/day inadults and 5 or 10 mg/day in the elderly or patients with hepaticimpairment. Chronic treatment with hypnotic drugs such as zopiclone andzolpidem, appears to produce more limited change in GABA-A receptorsubunit expression. It has been shown that the hypnotic efficacy ofzolpidem is generally comparable to that of the benzodiazepinesflunitrazepam, flurazepam, nitrazepam, temazepam and triazolam as wellas non-barbiturate and non-benzodiazepine hypnotic agents such aszopiclone and trazodone in the treatment of elderly and adult patientswith insomnia.

Zaleplon isN-[3-(3-cyanopyrazolo[1,5-a]pyrimidin-7-yl)phenyl]-N-ethylacetamide;zolpidem is N,N,6-trimethyl-2-p-toyl-imidazo[1,2,-a]pyridine-3-acetamideL-(+)-tartrate (2:1); zopiclone is6-(5-chloropyrid-2-yl)₅-(4-methylpiperazin-1-yl)carbonyloxy-7-oxo-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine;trazodone is 2-[3{4-(m-chlorophenyl)-1-piperazinyl]propyl]s-triazolo[4,3-a]-pyridine-3(2H)-one monohydrochloride.

Zolpidem, for example, is gaining favour worldwide because of itsefficacy and its side effect profile, which is milder and lessproblematic than that of the benzodiazepines and barbiturates used totreat insomnia. There is little evidence of rebound insomnia orwithdrawal symptoms after discontinuation of the drug when it is givenas recommended (10 mg/day for <1 month) or over longer periods.Initially, there were no reports of tolerance developing to the hypnoticeffects of zolpidem in a number of studies of up to 6 months duration.Still, side effects (delirium, hallucinations) are not uncommon withzolpidem use and It may have a marked dependence potential. Yet, in arecent report of a WHO Expert Committee responsible for reviewinginformation on dependence-producing drugs to assess the need for theirinternational control, zolpidem was recommended for internationalcontrol. Lowering the risk of developing dependence is thus a publichealth issue.

Daily cycles in physiology and behaviour appear to be a universalfeature of living organisms. An intrinsic body clock residing in thebrain's suprachiasmatic nucleus (SCN) regulates a complex series ofrhythms including sleep-wakefulness. The individual period of theendogenous clock is either slower or faster than the solar 24-hday/night cycle (in humans it is usually >24 h) and is normallyentrained by the 24-h light dark cycle to match the environmentalrhythm. Light is the ubiquitous signal for resetting the timing of theclock. An important output signal generated by the SCN is the inductionof synthesis of the pineal hormone melatonin(N-acetyl-5-methoxytryptamine) at night. Melatonin is directly regulatedby the SCN and thus serves as a marker of the circadian clock phase; butit can also relay time-of-day information (signal of darkness) tovarious organs, including the SCN itself. The phase shifting effects ofmelatonin are essentially opposite to those of light. Thus, melatonin,given several hours before its endogenous peak at night, effectivelyadvanced sleep time in delayed sleep phase syndrome patients andadjusted the sleep wake cycle to 24 h in the blind, where light therapyis inapplicable. Melatonin and light, when properly timed (namely lightin the subjective night and melatonin in the subjective day of theinternal clock) may also alleviate jet lag and sleep in night-shiftworkers trying to sleep during daytime.

Melatonin plays a major role in the induction and regulation of sleep.The sleep promoting activity of melatonin in humans is best demonstratedin daytime, when the hormone is not produced endogenously, or insubjects who suffer from abnormal melatonin production due to agingdisease or use of certain drugs (e.g. beta adrenoceptor blockers). Anumber of pharmacodynamic interactions between melatonin andbenzodiazepine-mediated behavioral effects have been reported.Benzodiazepine therapy has been found to suppress the nocturnal rise inplasma melatonin and shift its day-night rhythmicity; this suppressionmay interfere with normal sleep-wake rhythmicity and add-on melatoninreplacement may help maintain the efficacy of benzodiazepine hypnotics.Thus, administration of sustained release melatonin (2 mg) to 23 chronicbenzodiazepine-using elderly insomniacs, resulted in a significantimprovement in sleep maintenance and total sleep time compared toplacebo.

Besides replenishing the endogenous melatonin levels, melatonin was alsoreported to allow reduction of the therapeutic dose of thebenzodiazepine triazolam by 50% while maintaining its hypnotic activity.These results could be ascribed to additive effects of melatonin andbenzodiazepines of sleep induction. Most importantly, the sleepinducing, anxiolytic and anticonvulsant properties of melatonin are notmediated by the benzodiazepine receptor, since flumazenil, abenzodiazepine-antagonist, administered concomitantly was unable toblock melatonin's effects.

Melatonin is also an effective aid in withdrawal for addictive drugs,including benzodiazepines. A strong proof of melatonin's efficacy inwithdrawal from an addictive drug has been found when applied innicotine withdrawal, which is usually accompanied by negative mood andperformance. In addition, administration of melatonin enabled rapiddiscontinuation of benzodiazepine therapy in a 43-year-old woman who wasbenzodiazepine addicted. The effects of concomitant sustained releasemelatonin (2 mg/day), compared to placebo, in facilitatingbenzodiazepine discontinuation, was assessed in 34 adult volunteers(40-90 years old) with insomnia, who had been long term benzodiazepineusers. The results indicated that sustained release melatonineffectively facilitated discontinuation of benzodiazepine, whilemaintaining good sleep quality during the tapering-off period; by theend of the tapering-off period, 14 of 18 subjects who had receivedmelatonin, but only 4 of 16 in the placebo group, discontinuedbenzodiazepine (p=0.006). Sleep quality scores were significantly higherin the sustained release melatonin group (p=0.04). No serious adverseevents were noted. The use of melatonin for discontinuation of drugdependencies has been described, e.g., in our European Patent No.0724878 B1.

Suhner et al., in Aviat. Space Environ. Med. 72: 638 (2001), reportedthat co-administration of zolpidem 10 mg with regular release melatonin5 mg, for jet-lag, was less effective than zolpidem alone and lesswell-tolerated than melatonin. The co-administered drugs caused variousside-effects such as nausea, vomiting, amnesia and somnambulia to thepoint of incapacitation thus suggesting that co-administration ofzolpidem and melatonin would be unlikely to be of practical therapeuticuse in treating conditions such as insomnia, which are related to thecircadian rhythm.

However, it has unexpectedly been found in accordance with the presentinvention, that melatonin potentiates the effects of the non-barbiturateand non-benzodiazepine hypnotics such as zolpidem, on sedation as wellas on psychomotor skills. The interaction was not additive, and it wasnot due to a pharmacokinetic change in blood concentrations of eitherzolpidem or melatonin. Most importantly, the pharmacodynamic interactionwas transient and disappeared within 2 hours, while the concentrationsof both drugs in blood were still high.

SUMMARY OF THE INVENTION

The present invention thus provides in one aspect, use of melatonin inthe manufacture of a medicament effective for the short-termpotentiation of the hypnotic effect of at least one compound selectedfrom the group consisting of non-barbiturate and non-benzodiazepinehypnotics.

In another aspect, the invention provides a pharmaceutical formulationwhich comprises, in addition to at least one carrier, diluent, coatingor adjuvant: at least one compound selected from non-barbiturate andnon-benzodiazepine hypnotics, and melatonin in an amount and formeffective for short term potentiation of the hypnotic effect of the atleast one compound.

The medicament or pharmaceutical formulation is preferably furthercharacterized by at least one of the following features:

-   (a) the hypnotics are GABA-A receptor modulators;-   (b) the hypnotics are compounds which include a fused-ring system    containing ring nitrogen;-   (c) the medicament or pharmaceutical formulation comprises at least    one carrier, diluent, coating or adjuvant;-   (d) the medicament or pharmaceutical formulation is in unit dosage    form;-   (e) the medicament or pharmaceutical formulation includes at least    one compound selected from the group consisting of non-barbiturate    and non-benzodiazepine hypnotics;-   (f) the at least one compound is present in the medicament or    pharmaceutical formulation, in an amount which, if administered in    absence of melatonin, would be a sub-therapeutic amount;-   (g) the medicament or pharmaceutical formulation is adapted for    sustained release of melatonin.

DEFINITION

The term “short term potentiation” means potentiation for a period ofnot more than about 4 hours, preferably not more than about 2 hours, andparticularly for a period of about one hour, +25%.

DETAILED DESCRIPTION OF THE INVENTION

The present invention focuses on the concept of combined use ofmelatonin and a therapeutic or sub-therapeutic dose of a non-barbiturateand non-benzodiazepine hypnotic so as to effectively promote sleepinitiation for patients who have difficulty falling asleep, whilereducing the risk of memory impairments, psychomotor performanceaccidents, and subsequent tolerance and dependence.

The medicament or pharmaceutical formulation preferably includes atleast one acrylic resin and is adapted for sustained release ofmelatonin; desirably, it is further adapted for regular release of saidat least one compound.

In this connection, the sustained release properties may be achieved,e.g., by at least one of the following features, namely:

-   (a) by variation in the particle size of the melatonin;-   (b) by use of at least two different coating materials which    dissolve at different rates in the human body; and/or-   (c) by varying the thickness of coating material(s) whereby the    particulate melatonin is coated with different thicknesses of    coating material(s) which dissolve at different rates in the human    body.

The at least one compound selected from non-barbiturate andnon-benzodiazepine hypnotics preferably comprises a bicyclic fused ringsystem, e.g. one including at least two ring nitrogen atoms.

Exemplary such ring systems are:

-   -   the pyrazolo[1,5-a]pyrimidine skeleton, e.g. the hypnotic        zaleplon;    -   the imidazo[1,2,-a]pyridine skeleton, e.g. the hypnotic        zolpidem;    -   the pyrrolo[3,4-b]pyrazine skeleton, e.g. the hypnotic        zopiclone; and    -   the triazolo[4,3-a]-pyridine skeleton, e.g. the hypnotic        trazodone.

The invention will now be illustrated by the following non-limitingExamples.

EXAMPLE 1

Method. The pharmacokinetics of melatonin (2 mg sustained releaseformulation), zolpidem (10 mg) and their combination were assessed in 16volunteers (12 males and 4 females). The mean age of the enrolledsubjects was 59.4 years (SD 3.2), the mean Body Mass Index was 25.5kg/m2 (SD 2.3), the mean weight was 75.8 kg (SD 11.8) and the meanheight was 171.8 cm (SD 7.7). In a randomized, double-blind, crossoverstudy, the subjects were given a tablet of placebo in the evening toestablish baseline and then a tablet of melatonin, zolpidem, or acombined dose or placebo, in a random order in the evening (one nightonly), with a one week washout between treatments.

Blood samples were withdrawn from the subjects at pre-selected intervalsafter the administration of the tablets.

Results. The pharmacokinetic parameters of the two drugs when givenalone and in combination are presented in Table 1: TABLE 1Pharmacokinetic parameters of melatonin (sustained release 2 mg) andzolpidem (10 mg) when given alone and in combination Melatonin inZolpidem in Drug Pharmacokinetic serum serum given parameter Mean (SD)Mean (SD) Melatonin Area under the 5.91 (3.3) ng/ml curve Zolpidem Areaunder the — 0.88 (0.61) mcg/ml curve Melatonin + Area under the 5.95(3.9) ng/ml  1.1 (0.7) mcg/ml zolpidem curve Melatonin Time to 1.88(1.4) h maximum Zolpidem Time to  1.8 (1.2) h maximum Melatonin + Timeto 2.13 (1.3) h  2.0 (1.1) h zolpidem maximum Melatonin maximum 1.21(0.6) ng/ml concentration Zolpidem maximum — 0.22 (0.11) mcg/mlconcentration Melatonin + maximum 1.26 (0.8) ng/ml 0.19 (0.05) mcg/mlzolpidem concentrationAll P values of combination compared to individual drug > 0.5 (nosignificant differences).

Conclusions. After concomitant administration of sustained releasemelatonin and zolpidem, melatonin absorption is similar to the resultsafter single dosing of sustained release melatonin. After singleadministration of zolpidem 10 mg, plasma concentration values ofzolpidem are comparable to those after co-administration of zolpidemwith sustained release melatonin. Based on the lack of pharmacokineticinteraction, there should be no differences in efficacy of zolpidem whengiven concomitantly with melatonin.

EXAMPLE 2

Method. The effects of melatonin (2 mg sustained release formulation),zolpidem (10 mg), their combination and placebo, on psychomotor skillsand driving performance, were assessed in 16 volunteers (12 males and 4females). The mean age of the enrolled subjects was 59.4 years (SD 3.2),the mean Body Mass Index was 25.5 kg/m2 (SD 2.3), the mean weight was75.8 kg (SD 11.8) and the mean height was 171.8 cm (SD 7.7).

In a randomized, double-blind, crossover study the subjects were given atablet of placebo in the evening to establish baseline and then a tabletof melatonin, zolpidem, their combination, or placebo, in a random orderin the evening with one week with no treatment in between treatments. Abattery of performance tests and driving skill tests were given to thepatients at pre-selected intervals after the administration of thetablet. These included psychomotor tasks for reaction test, vigilanceand co-ordination: ARCI 49, Grooved Pegboard, Rivermead story, picturepresentation, simple reaction time, digit vigilance task, choicereaction time, delayed picture recognition, visual tracking, drivingsimulator: highway driving and wake-EEG.

Results.

Cognitive Drug research tests: No cognitive effects of sustained releasemelatonin dosed alone, adverse or otherwise were identified. There wereseveral acute impairments seen with zolpidem compared to placebo, whichwere resolved by 12.5 hours post-dosing. The effects found with zolpidemalone, were seen across measures of attention, episodic secondary memoryand motor co-ordination. When sustained release melatonin and zolpidemwere co-dosed, in placebo comparisons impairments were seen for allmeasures at 1 hour, some of these persisting until 4 hours. At 1 hourpost-dose, the impairments with co-dosing were significantly greaterthan those produced by zolpidem alone, and must therefore be consideredsynergistic interactions. At 4 hours, the impairments seen withco-dosing were similar to the effects of zolpidem alone at this time. Atthe 12.5 and 15 hours post-dose, there is no evidence for any effects ofco-dosing the two compounds.

ARCI49: a decrease of euphoria (MBG scale) was observed 1 hourpost-dosing with all groups. Four hours after administration, thiseffect was more pronounced with the three treatment groups as comparedto placebo. An increase of dullness or slow-wittedness (LSD scale) wasobserved during the 4 hours post-dosing, for the three treatment groupscompared to placebo. A strong significant sedative effect was noticed(increase of the PCAG scale) during the first 4 hours post-dosing in thezolpidem 10 mg and the sustained release melatonin 2 mg+zolpidem 10 mggroups, as compared to placebo. In the combined group, this effectreached the maximum at about 1 hour after administration, while in thezolpidem group, this effect increased gradually to reach the samemaximal value only at about 4 hours post-dosing. Concerning thesustained release melatonin 2 mg group, a slight increase was alsoobserved at about 4—hours post-dosing, but this effect, was rotsignificant as compared to placebo. Finally, a similar decrease of theempirical excitation (BG scale) was also noticed during the first 4hours post-dosing in the zolpidem 10 mg and the sustained releasemelatonin 2 mg+zolpidem 10 mg groups, as compared to placebo. Thiseffect corroborates the sedative effect observed. All these effects hadcompletely passed by the next morning (at 12 h30 and 15 hourspost-dosing).

Rivermead story: memory efficiency was decreased with zolpidem 10 mg andsustained release melatonin 2 mg+zolpidem 10 mg, for both recalls(immediate and delayed), compared to placebo and sustained releasemelatonin 2 mg. Immediate retrieval performance was more disturbed withzolpidem 10 mg+sustained release melatonin 2 mg, than with zolpidem 10mg alone, while the impairment on delayed recall (amnesic effect) wasequivalent in the two treatment groups. This amnesic effect observed inthese two treatment groups was essentially linked to zolpidem. Indeed,sustained release melatonin 2 mg seems to potentiate the effect ofzolpidem 10 mg concerning the performances in immediate memory but notfor delayed memory.

Grooved Pegboard: results observed in the Grooved Pegboard test showed aslowing of the execution of the task for both hands though the finemanual coordination is not disturbed. Indeed, for both conditions (ipsiand contra lateral) a significant increase of the duration was observedat 1 and 4 hours post-dosing in the zolpidem 10 mg and sustained releasemelatonin 2 mg+zolpidem 10 mg groups, compared to baseline and the twoother treatments (placebo and sustained release melatonin 2 mg). Thisincrease was more pronounced in the combined treatment group, suggestingthat sustained release melatonin 2 mg potentiates the effects ofzolpidem 10 mg. The main slowing effect appears at 1 h post-dosing andthen decreases over the time.

Driving simulator: no significant difference was observed on medians ofthe investigated parameters (absolute speed, deviation from the speedlimit and deviation from the ideal route). However, significantdifferences were noticed for the standard deviations of theseparameters, and the number of collisions. Indeed, the standarddeviations for the absolute speed and the deviations from the speedlimit and ideal route parameters, were increased at 2 hours post-dosingwith zolpidem 10 mg and zolpidem 10 mg+sustained release melatonin 2 mg.For absolute speed parameter, this effect was even more pronounced inthe combined treatment group. These standard deviation increases suggestthat driving is irregular, fluctuating not only for the speed but alsofor the road holding. The variations observed for the ideal routeparameter, corroborate with the increased number of collisions countedat 2 hours post-dosing, in zolpidem 10 mg and sustained releasemelatonin 2 mg, compared with zolpidem 10 mg groups. By the nextmorning, this driving irregularity had disappeared, and the number ofcollisions was similar to the placebo and sustained release melatonin 2mg treatment groups. At 13 hours after administration, neither drugdisturbs driving abilities.

Wake EEG: In resting conditions, no major differences in alpha activityhave been observed for sustained release melatonin compared to placebo.The decreases in alpha seen with zolpidem alone or zolpidem+sustainedrelease melatonin, are in agreement with the sedative potential ofzolpidem. In driving conditions, alpha activity was significantlyincreased under zolpidem or zolpidem+sustained release melatonincompared to sustained release melatonin alone (but not placebo).Compared to placebo, zolpidem has an increased theta rhythm on frontalleads, which is interpreted as an additional sign of sleep-inducingeffects.

On Day 2, some effects revealing reduced vigilance remain present undereyes-closed conditions, which could be due to resting. Indeed, theseeffects were abolished under active conditions while driving orperforming cognitive tests.

The most common treatment-emergent adverse event that occurred in thisstudy was somnolence. The incidence of somnolence was similar withzolpidem and zolpidem+sustained release melatonin, but had clearlyincreased compared with melatonin alone and placebo. There seems to be apotentiation of central effects of zolpidem by concomitant intake ofsustained release melatonin, since the intensity of adverse events wasmore severe with the combined treatment than with zolpidem alone;however, sustained release melatonin alone was well tolerated.

Conclusions. The effects of sustained release melatonin 2 mg treatmenton performance, memory and sedation are comparable on most parameters tothose observed with placebo. The present study has clearly identified atransitory pharmacodynamic interaction between sustained releasemelatonin and zolpidem, particularly at 1 hour following co-dosing. Thishad largely passed by 4 hours although the levels of the two drugs werestill high in plasma, and had completely passed by 12.5 and 15 hours.

When associated with melatonin sustained release 2 mg, the impairmentsobserved with zolpidem on mood, skill and cognitive aspects areemphasized particularly by 1 hour post-dosing. It should be noted thatthese interactions are potentially of clinical importance, because theyshould allow short-term potentiation of the effects of sub clinicaldoses of zolpidem, particularly during the first hour after dosing, whenit is advantageous for sleep induction and also reduces the risk offurther impairments by zolpidem, in view of subsequent non-potentiation.

Zolpidem treatment resulted in a significant worsening in driving skillsand memory tasks in the first hours of its administration, whereas theeffect of melatonin was not different from those of placebo treatment.These studies show that improvement in quality of sleep reported bypatients (as is the case with zolpidem) does not necessarily indicateenhanced restorative sleep if it is not associated with improved daytimevigilance.

It should be noted that a sustained release melatonin formulation is ofspecial interest in this respect, as it has been proven to improve sleepquality in patients with insomnia aged 55 and older, with a subsequentimprovement in daytime vigilance. Melatonin is however not perceived bypatients as improving sleep initiation and that aspect is well providedby zolpidem. These facts will be important for designing a new hypnotictreatment with a better safety/efficacy profile.

The present invention contemplates co-administration of melatonin andthe defined hypnotic, such as zolpidem. The term co-administration inthis context, the purpose of which is to achieve an improved clinicaloutcome, may be practised by administering separate dosage forms ofmelatonin and hypnotic, or a combined dosage form. An illustrativeExample of the preparation of a combined dosage form follows. It will beappreciated, however, that other known methods may be used for preparinga combined dosage form, such as, for example, the methods described inU.S. Pat. No. 6,174,873 B1, the entire contents of which areincorporated by reference herein.

EXAMPLE 3

In this Example, a two-layer tablet is prepared, which is sustainedrelease in respect of melatonin (inner core), but regular release inrespect of the exemplary hypnotic, zolpidem (outer layer). Because theouter layer undergoes immediate dissolution in the enteric system, theprofile of zolpidem generated will resemble that given in Example 1,whereas because the core tablet will dissolve gradually, the profile ofmelatonin generated in the blood will be similar to that of Example 1also.

Method. A sustained release core melatonin tablet was first prepared bymixing together the following ingredients and compressing the mixture ina 7 mm cylindrical punch, at 2.5 tons, namely, melatonin (2 mg/tablet),and Eudragit RSPO acrylic resin carrier (Rohm Pharma), lactose andcalcium hydrogen phosphate, in an approximately 2:1:2.5 ratio by weight.

An aqueous coating spray suspension is then prepared by suspending anacrylic resin (Eudragit RD 100), polysorbate 80 and talc in anapproximately 10:2:5 ratio by weight, and zolpidem tartrate (5mg/tablet) in 6 ml water per 1 g solid. The core tablet is then sprayedwith the suspension to a 2 mm dried coating thickness, thus forming acoated tablet.

While this formulation should be administered in accordance with aphysician's instructions, it is presently contemplated that two suchtablets taken two hours before bedtime would be appropriate.

Sustained release melatonin has an effect of its own on sleep. This isdemonstrated by an improvement in restorative sleep (improvement ofsubjective quality of sleep and subsequent improvement in daytimevigilance) as we have recently described in the patent on the use ofmelatonin to improve quality, and is given here as Examples 4, 5 and thedelay in the cortisol peak towards the morning hours that is seen withthe sustained release but not with the regular release formulation(Example 6). This effect may be responsible for the enhancement ofrestorative sleep.

EXAMPLE 4

Method. The effect of a sustained release formulation of melatonin onsleep quantity and quality in 40 elderly primary insomnia patients (aged76 years) (SD 8), were studied in a randomized, double-blind, twoparallel group study. The subjects were treated for 3 weeks everyevening with melatonin (2 mg sustained release formulation) or placebo.Full-night polysomnographic recordings were performed on the last twodays of treatment to measure quantitative aspects of sleep. On eachmorning following sleep recording in the laboratory, a battery ofpsychomotor tests was taken by all patients to assess daytime vigilance.In addition, patients recorded every day in diaries their perceivedquality of sleep the previous night.

Results. The results show beneficial effects of melatonin on sleepinitiation, similar to the effects of hypnotic drugs. In contrast tothis apparently hypnotic effect, psychomotor skills were significantlyhigher in the melatonin group compared to the placebo-treated group:Significant treatment effects for the Critical Flicker fusion test andTotal Reaction Time under melatonin vs. placebo were observed at the endof treatment.

Conclusions. These results thus show for the first time the associationof hypnotic effect (shortening of sleep latency) by melatonin withenhanced daytime vigilance in primary insomnia patients, suggesting thatthe restorative value of sleep has increased in these patients. Whenusing hypnotic drugs, shortening of sleep latency and improved qualityof sleep is associated with impaired psychomotor skills in the morning,or at best no significant deterioration. No hypnotic drug has ever beenshown to increase daytime vigilance. Surprisingly, in their diaries,patients did not evaluate the ease of getting to sleep as being betterwith melatonin compared to placebo. In fact, the patients judged theirquality of sleep to be improved with melatonin but not placebotreatment. The restorative value of sleep may thus be associated with aperceived improvement in quality of sleep.

EXAMPLE 5

Method. The effect of a sustained release formulation of melatonin onsubjectively assessed sleep quality and daytime vigilance in 170 elderlyprimary insomnia patients (aged 68.5 years) (SD 8.3) was studied in arandomized, double-blind, two parallel group study. The subjects weretreated for 2 weeks with placebo to establish baseline characteristicsand then for 3 weeks with melatonin (2 mg per night of sustained releaseformulation) or placebo. On the last three days of the baseline andtreatment periods patients were asked to assess the-quality of theirsleep the previous night and their feeling in the morning. The qualityof sleep question was “How would you compare the quality of sleep usingthe medication with non-medicated (your usual) sleep?” The patientsmarked the level of their perceived quality of sleep on a 100 mm,non-hatched horizontal line with two endpoints. The left endpointlabeled “more restless than usual” and the right endpoint is labeled“more restful than usual”. The waking state question was “How do youfeel now?” The patients marked the level of their perceived waking stateon a 100 mm, non-hatched horizontal line with two endpoints. The leftendpoint labeled “tired” and the right endpoint is labeled “alert”. Thedistance of the patient mark from the right endpoint in mm was measured.(a reduction in value therefore indicates a better sleep or less tiredstate). The mean distance across the three nights was calculated.

Results. It was found that both quality of sleep and daytime alertnesssignificantly improved with sustained release melatonin compared toplacebo (Table 2) showing a link between improved restful sleep and lessfatigue in the morning. TABLE 2 Effects of sustained release melatoninand placebo on subjectively assessed quality of sleep and daytimealertness in primary insomnia patients. Placebo, Melatonin, changechange in mm Response in mm mean (SE) mean (SE) Change in perceivedquality of −24.3 (2.6)* −17.6 (2.1) sleep Change in perceived daytime−16.8 (2.7)*  −6.6 (2.0) alertness*The difference from placebo is significant (p < 0.05)

Conclusions. These results show that melatonin enhanced the restorativevalue of sleep in these primary insomnia patients.

EXAMPLE 6

Method. The following experiments were performed in a double-blind,placebo controlled crossover fashion. Each patient received all threekinds of tablets (placebo, regular release and sustained release), butin random order not known to the patient or the staff.

Results. Administration of melatonin (2 mg) in a sustained releaseformulation (SR-Mf), once daily at 10 PM, for one week, to eight healthyelderly persons suffering from insomnia, resulted in a significantincrease in their sleep efficiency but not sleep latency. (Sleepefficiency is the amount of time spent asleep from total time in bed;sleep latency is the time taken to fall asleep from first lights-off).On the other hand, treatment of the same individuals with melatonin (2mg) in a regular release formulation (RM) did not improve sleepefficiency but shortened sleep latency compared to placebo treatment ofthe same subjects. These results can be explained by the short half-lifeof melatonin in the blood. Namely, the sustained release formulationproduces lower blood levels of the hormone for extended periods of timeand thus its effects may start slowly but are significant later onduring the night.

The cortisol level in these patients was assessed by urinary excretionof the hormone at 2 hour intervals over a 24 hour period. In the placebotreatment group, patients displayed a cortisol rhythm which reached itspeak at 8:36 AM and the cortisol then declined, as is known for subjectsabove 40 years of age. The mean 24 hour excretion rate/hour (whichapproximated blood concentrations) of the cortisol in urine in thecontrol group was 3.2 microgram/hour. The amplitude of the rhythm (i.e.maximal deviation of the mean 24 h to maximum or minimum excretion rate)was 1.8 mg/hour.

After treatment for 1 week with the regular release melatonin theoverall amount of cortisol excreted was reduced. The mean 24 hourexcretion rate decreased to 2.5 mg/hour and the amplitude decreased to1.0 mg/hour. In addition there was a slight backwards shift in the timeof the peak, which occurred at 8:27 AM. Anticipation of the cortisolrhythm after administration of regular release melatonin is compatiblewith observations made by Terzolo et al., J. Pineal Research, 1990, 9:113-124. However, a decrease in mean 24 hour-levels and amplitude of thecortisol rhythm was not observed by Terzolo.

After one week's treatment with sustained release melatonin, it wasfound that like the regular melatonin, secretion of cortisol wasattenuated (mean 24 h rate was 2.5 mg/hour) and the amplitude 1.2mg/hour (as with the regular release), but the peak was delayedsignificantly to later in the day and occurred at 12:06 PM. Thus, thepeak was delayed by administration of sustained release melatonininstead of being the same or slightly advanced. The same cortisolprofile was also found in these patients-after 1 month's treatment withthe sustained release formulation (mean 24 hour excretion 2.5 mg/hour,amplitude 1.0 mg/hour and peak time 12:08 hours).

Conclusions. These results show that the response of the body tomelatonin is not obvious: the body reads the melatonin profile and notjust the fact that it is present at some time. Interestingly, in humansyounger than 40 years, it is known that the cortisol rhythm is alsodelayed compared to older individuals. Hence, the cortisol profilegenerated in the elderly after the sustained release melatonin treatmentis similar to that in younger individuals.

Discussion. An inverse relationship has been documented in humansbetween cortisol and quality of sleep, i.e. as sleep quality andquantity decline, levels of the adrenal hormone cortisol increase. Itmay be noted that cortisol is a stress hormone, and its high levels atnight may prevent restorative sleep. The present experiment shows thatadministration of regular release melatonin can lower cortisolproduction, but that administration of sustained release melatonin bothlowers the cortisol level and delays its peak and thus can improve sleepduring the dawn hours.

With hypnotic drugs as defined for the purpose of the present invention,such as zolpidem, it is crucial that elimination will be rapid and thatno drug will remain in the morning. Because the drug only affects theinitiation of sleep, it is useful to augment its effects in the firsthour so as to get maximal efficacy with a lower dose and avoid itsdetrimental effects later on in the night. The intrinsic effects ofmelatonin, when co-administered with e.g. zolpidem, are maintained. Thecombination of melatonin and zolpidem will thus allow improvement ofsubjective sleep latency (that is not perceived with melatonin alone)while avoiding the bad effects of zolpidem later on in the night (onmemory and coordination).

EXAMPLE 7

Method. The effect of a sustained release formulation of melatonin onsubjectively assessed sleep quality and daytime vigilance in 5 primaryinsomnia patients aged 55 years and older, who were already taking 10 mgzolpidem per night, were studied. The subjects were treated for 2 weekswith placebo to establish baseline characteristics and then for 3 weekswith melatonin (2 mg per night of sustained release formulation). On thelast three days of the baseline and treatment periods patients wereasked to assess the quality of their sleep the previous night. Thequality of sleep question was “How would you compare the quality ofsleep using the medication with non-medicated (your usual) sleep)?” Thepatients marked the level of their perceived quality of sleep on a 100mm, non-hatched horizontal line with two endpoints. The left endpoint islabeled “more restless than usual” and the right endpoint is labeled“more restful than usual”. The distance of the patient mark from theright endpoint in mm was measured. (a reduction in value thereforeindicates a better sleep or less tired state). The mean distance acrossthe three nights was calculated. Response was defined as a meanimprovement in the 3 nights of 10 mm on the 100 mm visual analog scales.

Results. It was found that 3 of the 5 patients that were taking zolpidemresponded to the concomitant therapy with melatonin (60%). This value isequivalent to that obtained in parallel studies with patients who hadnot been taking zolpidem concomitantly.

Conclusions. The improvement of quality of sleep upon concomitanttherapy with melatonin can be ascribed to melatonin and not zolpidem,since patients were taking zolpidem already at baseline. In addition,the synergy between the two drugs is particularly evident in the firsthour after administration and should not affect the all night sleepquality. Moreover, these data show that the clinical efficacy ofmelatonin (after the synergy period) is maintained when givenconcomitantly with zolpidem.

Discussion. Since it is known that zolpidem does not alter the profileof endogenous melatonin, and that melatonin does not bind to thebenzodiazepine receptor, it is clear that the potentiation (or synergy)in accordance with the present invention, is due neither to replacementof melatonin deficiency by zolpidem, nor to binding of both agents tothe same receptor.

While particular embodiments of the invention have been particularlydescribed hereinabove, it will be appreciated that the present inventionis not limited thereto, since as will be readily apparent to skilledpersons, many variations and modifications can be made. Such variationsand modifications which have not been detailed herein are deemed to beobvious equivalents of the present invention. For example, structuralanalogs of melatonin which substantially imitate the function ofmelatonin in the human body are deemed to be obvious chemicalequivalents of melatonin. The essential concept, spirit and scope of thepresent invention will be better understood in the light of the claimswhich follow.

1-28. (canceled)
 29. A method of potentiating the hypnotic effect of atleast one compound selected from the group consisting of non-barbiturateand non-benzodiazepine hypnotic compounds in a human in need thereofwhich comprises administering melatonin in combination with saidhypnotic compound in an amount effective to potentiate said compound'shypnotic effect.
 30. The method of claim 29, in which said melatonin andsaid hypnotic compound are administered in a single pharmaceuticalformulation.
 31. The method of claim 30, which is further characterizedby at least one of the following features: (a) said hypnotics are GABA-Areceptor modulators; (b) said hypnotics are compounds which include afused-ring system containing ring nitrogen; (c) said formulationcomprises at least one carrier, diluent, coating or adjuvant; (d) saidformulation is in unit dosage form; (e) said formulation includes atleast one compound selected from the group consisting of non-barbiturateand non-benzodiazepine hypnotics; (f) said at least one compound ispresent in said medicament and in an amount which, if administered inabsence of melatonin, would be a sub-therapeutic amount; (g) saidformulation is adapted for sustained release of melatonin.
 32. Themethod of claim 31, wherein said formulation includes at least oneacrylic resin and is adapted for sustained release of melatonin.
 33. Themethod of claim 32, wherein said formulation is further adapted forregular release of said at least one compound.
 34. The method of claim29, 30 or 31, wherein said at least one compound comprises a bicyclicfused ring system.
 35. The method of claim 34, wherein said bicyclicfused ring system includes at least two ring nitrogen atoms.
 36. Themethod of claim 35, wherein said bicyclic ring system comprises apyrazolo[1,5-a]pyrimidine, imidazo[1,2,-a]pyridine,pyrrolo[3,4-b]pyrazine or triazolo[4,3-a]-pyridine skeleton.
 37. Themethod of claim 36, wherein said at least one hypnotic compound isselected from the group consisting of zaleplon, zolpidem, zopiclone andtrazodone.
 38. A pharmaceutical formulation which, in addition to atleast one carrier, diluent, coating or adjuvant, comprises the followingactive ingredients: at least one compound selected from the groupconsisting of non-barbiturate and non-benzodiazepine hypnotics, andmelatonin in an amount and form effective for short term potentiation ofthe hypnotic effect of said at least one compound.
 39. Thepharmaceutical formulation of claim 38, which is further characterizedby at least one of the following features: (a) said hypnotics are GABA-Areceptor modulators; (b) said hypnotics are compounds which include afused-ring system containing ring nitrogen; (c) said formulation is inunit dosage form; (d) said at least one compound is present in saidformulation in an amount which, if administered in absence of melatonin,would be a sub-therapeutic amount; (e) said formulation is adapted forsustained release of melatonin.
 40. The pharmaceutical formulation ofclaim 39, which includes at least one acrylic resin and is adapted forsustained release of melatonin.
 41. The pharmaceutical formulation ofclaim 40, which is further adapted for regular release of said at leastone compound.
 42. The pharmaceutical formulation of claim 39 or 40,wherein said non-barbiturate and non-benzodiazepine hypnotics comprisesa compound in which said fused ring system is a bicyclic ring system.43. The pharmaceutical formulation of claim 42, wherein said bicyclicring system includes at least two ring nitrogen atoms.
 44. Thepharmaceutical formulation of claim 43, wherein said bicyclic ringsystem comprises a pyrazolo[1,5-a]pyrimidine, imidazo[1,2,-a]pyridine,pyrrolo[3,4-b]pyrazine or triazolo[4,3-a]-pyridine skeleton.
 45. Thepharmaceutical formulation of claim 44, wherein said at least onehypnotic is selected from zaleplon, zolpidem, zopiclone and trazodone.46. A method of decreasing the dose of a non-barbiturate ornon-benzodiazepine hypnotic compound administered to a person in need ofsaid hypnotic compound without lessening said compound's desiredhypnotic effect which comprises administering to said person melatoninin combination with a lower dose of said agent, wherein said melatoninis administered in an amount effective to potentiate the hypnotic effectof said compound such that said desired hypnotic effect is achieved. 47.A method of lessening the risk of the development of tolerance to ordependence on a non-barbiturate or non-benzodiazepine hypnotic compoundin a person administered said compound which comprises administering tosaid person melatonin in combination with said hypnotic compound,wherein said melatonin is administered in an amount sufficient topotentiate hypnotic effects of said compound such that a desiredhypnotic effect can be obtained with a lower dose of said compound thanif said compound was administered in the absence of said melatonin.